HDACs are zinc metalloenzymes that catalyse the hydrolysis of acetylated lysine residues. In histones, this returns lysines to their protonated state and is a global mechanism of eukaryotic transcriptional control, resulting in tight packaging of DNA in the nucleosome. Additionally, reversible lysine acetylation is an important regulatory process for non-histone proteins. Thus, compounds which are able to modulate HDAC have important therapeutic potential.
WO2010/086646 discloses compounds which act as inhibitors of HDAC. The heteroaryl capping groups and the zinc-binding groups are joined via an alkylene linker.
Co-pending PCT application number PCT/GB2014/051454 discloses the following compounds which are disclaimed from this application:
4-({[5-(6-Aminopyridin-3-Apyridin-2-yl](pyrazin-2-yl)amino}methyl)-N-hydroxybenzamide having the following structure.

4-({[5-(2-Aminopyridin-4-yl)pyridin-2-yl](pyrazin-2-yl)amino}methyl)-N-hydroxybenzamide having the following structure.

N-hydroxy-4-[({5-[2-(methylamino)pyridin-4-yl]pyridin-2-yl}(pyrazin-2-yl)amino)methyl]benzamide having the following structure.

N-hydroxy-4-{[(pyrazin-2-yl)[5-(pyridin-4-yl)pyridin-2-yl]amino]methyl}benzamide having the following structure.
